Woody



H. H. C. DUNWOODY.

CYCLOID PROPELLER.

APPLICATION FILED NOV- 28, I919.

Patented July 26, 1921.

UNITED STATES PATENT- oFF cE.

, Specification of Letters Patent.

CYGLOID PRorELLnR.

Patented July 26, 1921.

Application filed November 28, 1919. Serial No. 341,049.

T 0 all whom it may concern:

Be it known that I, HENRY H. C. DUN- WOODY, a brigadier general U. S. Army, re tired, a citizen of the United States, res1ding at Washington, in the District of Columbia, have invented certain new and useful Improvements in Cycloid Propellers; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. I

This invention relates to propellers especially adapted for aeroplanes, but also suitable for use in water or other fluids, and has for its object to improve the shape of the blades in such a manner that they will be more eflicient in action than is the case in propellers heretofore proposed.

With this and other objects in view the invention consists in the novel details of con struction that will be more fully hereinafter described and particularly pointed out in the claims.

Referring to the accompanying drawings forming a part of this specification, in which like numerals designate like parts in all the views Figure 1 is a diagram showing a common form of cycloid curve;

Fig. 2 is a cross section of a propeller blade showing cycloid curves on both sides of the same;

Fig. 3 is a conventional illustration of a two bladed propeller having a cycloidal cross section in its blades, the latter being long and slim as shown;

Fig. 1 is a conventional illustration of a three bladed propeller having cycloidal blades of a shape different from those in Fig. 3; and

Fig. 5 is a conventional view of a four bladed propeller having cycloidal blades of a different shape from those in Figs. 3 and 1.

1 indicates the well known cycloid generating circle, the point 2 of which will generate the cycloid curve 3, when the circle 1 is rolled on the track 4. Said curve 3 has certain well known properties which I employ in designing the cross sections of propeller blades in general.

That is to say, it is well known that the resistance of the air to a moving body increases as the square of the velocity, so that the air in contact with the surfaces of airplane propeller blades is under I a considerable compression. It is further well known that a body falling under the action of gravity will move from one point of a cycloid curve 3 to another point thereof in less: time than it will take to move between the same two points in any other curve. Therefore, if the cross sectional areas of any type of aeroplane propeller blades such as those indicated by the numerals 7 '8 and 9, are bounded by cycloidal curves or surfaces, such as 5 and 6, having difierent centers of curvature as shown particles of air under compression, due to the friction of the surfaces will traverse the said surfaces in a less time than would be the case with any other curved surface.

Another well known property of a cycloid resides in the fact that a body will fall through any arc of a cycloid in the same time whether it be great or small, and I take advantage of this fact in designing my blades to the end that a row of particles of the greatly compressed air will act on different sections of my blades through intervals of time that are more nearly equal than in the case of blades having difi'erently curved surfaces, and therefore, the

propelling effect of said blades due to the total action of the air from their outer tips to their roots will be greater than with any other form of curved surface. ,Since the time of travel of the air over the surfaces will be shorter and the total pressure greater, it is evident that the efficiency of my blades will be increased. In fact, the efiiciency of my blades will be found to be higher than the efiiciency of fiat surfaced blades, such as are indicated by the numeral 10 and shown in dotted lines in Fig. 2, for the churning action on the air is less with my blades in all cases.

The foregoing principles are of course also applicable to propellers acting in water, as will be clear from Fig. 2, wherein, supposing the shaft to turn in the direction of the arrow, the lower or entrance portion of the curve 6 first acts upon the water and the upper or last portions of the said curve continue to act upon it and to thus exert a most efiicient propelling effect, while the forward curved surface 5 maintains a relatively close contact, whereby a minimum churning action is experienced all as will be clear from the arrows 15 and 16, which are supposed to indicate the path of a particle of water being acted upon. In some cases I prefer the straight-edged blades shown in Fig 3, but in all'cases the said entrance or leading portions of the blades are thicker than are the following or rear ortions .of said plates as illustrated in Fig. 8. Tins difierence in thickness of the lower and upper portions of said blades is conveniently brought about by not only displacing the centers of curvature of the front and rest surfaces of the blades but also by I What I claim is:- I v 1. A propeller blade having a cross sectional area bounded by two cycloidal curves provided with cycloidal surfaces having different generating axes, and d'tfl'm'ent radii ofvgeneration, substantially as described.

3. A propeller adapted to operate in water each of whose blades has a cross section bounded by cycloidal curves having different centers of curvature and being of difierent thicknesses near their front and rear edge portions, substantially as described. V

Intestimony whereof I aifix my signature. r

HENRY H. C. DUNWOODY. 

